Generally chips are classified using a screen to give a chip analysis based on size rather than thickness. For example, TAPPI test RC16 superseded by useful method 21 (March 1974) specifies the use of an apparatus consisting of a plurality of screen plates mounted one on top of the other that are shaken for a period of time to classify the chips into the various size fractions.
A similar device has been designed for classifying chips in accordance with thickness, however, this device has not been generally accepted in the trade. It consists of a plurality of trays similar to that described hereinabove with respect to the TAPPI tests but with a plurality of parallel wires functioning as the screening elements. As in the TAPPI procedure, the trays are laid one upon another and shaken for a period of time to permit chips to be classified.
Other devices have been proposed for sorting or classifying chips in accordance with their thickness, however, to date, none have gained wide spread acceptance by industry because of their complicated nature, difficulty of operation and poor reliability. Thus there is no recognized standard chip thickness classification instrument or technique available.
It has been proposed to segregate mail by thickness using a rotary drum type apparatus as disclosed in Canadian Pat. No. 595,103 issued Mar. 8, 1962, Copping et al. In this device a plurality of plates are each mounted on a pair of brackets fixed one to each end of each plate and pivotedly mounted in a pair of annular end frame members to form the drum. The brackets are eccentrically weighted so that the plates pivot as the drum is rotated, thereby to increase the clearance between adjacent plates from a minimum clearance at the bottom to a maximum at the top of the rotation to free material trapped between adjacent plates so that it may fall back towards the centre of the drum. There is only a single setting whereby all the materials larger than a certain thickness will be retained and all the materials smaller than that thickness may pass between the adjacent plates.
It has also been proposed to grade beans utilizing a rotary drum type bean separator as disclosed in Canadian Pat. No. 788,300 issued June 25, 1968 to Grospety. The bean grader of this patent composed of a pair of end discs interconnected by fixed rods and expandable elements therebetween. The thickness or width of the expandable elements may be adjusted to vary the clearances between the expandable element and a pair of fixed transverse rods positioned one on each side of the expandable elements. The expansion is controlled by the position of a cam plate that can be moved axially relative to the drum to change the minimum expansion setting. The cam plate is provided with a camming surface that changes the expanded condition of the expandable members as the drum rotates, i.e. the expandable elements are at their maximum expansion for the particular cam setting during the bottom half of their rotation, and at a minimum thickness during the top half of their rotation the concept being that any materials wedged between the expandable members and the fixed rods will be released as the expandable members contract and will fall into the drum.
Neither the letter sorter of Canadian Pat. No. 594,103, nor the bean sorter Canadian Pat. No. 788,300 provide the means for separation capable of the classification of chips by thickness to provide a plurality of different thickness range fractions of the chips.